“We were doing a mall tour of different cities,” said the 24-year-old star of “The Mortal Instruments: City of Bones,” in theaters now. “And we were meeting all these fans, which is great, because they’re the people who are responsible for where we are.”

“One girl fainted when she saw Jamie,” Collins said of co-star Jamie Campbell Bower. Another showed Collins her runes — mystical marks, etched or tattooed onto the skin, and corresponding to those borne by the characters in the Cassandra Clare novels on which the movies are being based.

Better yet: “One named their baby after Jace,” Collins said of the character played by Bower, who — like Collins’ character, Clary Fray, is a Shadowhunter, dedicated to hunting down demons.

“It’s crazy,” the actress said, in a way one does when stating the obvious. “Maybe I wouldn’t name my baby after Jace, but people are passionate about these stories. And the first one’s not even out yet and they’re acting this way.”

The first one — “City of Bones” — is just the beginning of what everyone involved hopes will be a series to rival (or surpass) the “Harry Potter,” “Twilight” and “Percy Jackson” franchises: The author, Clare, has just finished the sixth in her kitchen-sink fantasy series, and while the first movie adaptation is still in theaters, Collins and company will start shooting the second (title: “City of Ashes.” The other books in the series are “MI: City of Glass,” “City of Fallen Angels,” “City of Lost Souls” and “City of Heavenly Fire”).

“We are signed up for three,” Collins said of her principal co-stars. “But when you take into account that is now publishing the sixth one, it could go longer. When you take on a series like this you can never assume it’s going to go that many, but you hope you’ll get the opportunity to do a character for as long as people want you to do it.”

The daughter of rocker Phil Collins, the actress was born in Surrey, England, but after her parents’ divorce moved with her mom to Los Angeles, where she was educated, majoring in broadcast journalism at University of Southern California. Having begun acting on British TV at age 2, Collins has more recently been seen in the fantastical “Mirror Mirror,” where she played Snow White to Julia Roberts’ evil Queen; “Priest,” in which Paul Bettany hunted vampires; and the less phantasmagorical “Stuck in Love” (formerly “Writers”) with Greg Kinnear and Jennifer Connelly, and “The English Teacher,” with Julianne Moore and Nathan Lane.

“The new Audrey Hepburn!” declared one UK website, after Collins did a retro-Hollywood photo spread for the London magazine Tatler. She does have a face for movies, though she doesn’t want them full of shadows and ghouls. Not all the time.

“Since I finished filming the first one,” she said of “Mortal Instruments,” “I did a film in Dublin called ‘Love, Rosie,’ which is really the opposite kind of movie, I play a mom, 10 years older, British. Since day one, from ‘The Blind Side’ to ‘Priest,’ ‘Mirror Mirror’ to ‘The English Teacher,’ I’ve made a conscious effort to switch it off and have people seeing me do different characters. Because the last thing I want is getting pigeonholed.”

It’s a comfortable trap. “But I think when you look at Jennifer Lawrence and Kristin Stewart,” she said, referring to the stars of “Hunger Games” and the “Twilight” movies, “they’ve been able to do a franchise and still do other things and have an identity aside from those movies.”

“Mortal Instruments” could offer a warm embrace, or a stranglehold: According to Publisher’s Weekly, Clare has 12 million books in print domestically, 24 million internationally, and her sales have jumped 150 percent since last year, presumably on the strength of the movie hype. Curiously enough, when the author was getting started, publishers wanted her to change her central character, Clary, from female to male. They had other reservations, too, in those pre-“Twilight” days (“City of Bones” was published in 2007; the initial “Twilight” movie was released in 2008).

“They said, ‘Who’s going to be interested in werewolves and vampires?’ ” Collins laughed. “I know, right? But Cassandra was very passionate and confident that having a young female heroine was important.”

What’s also important — and could be a key in whether “Mortal Instruments” takes off the way other demon-populated movie series have — is that the core story works in or out of the supernatural.

“It’s so great to portray a young woman who’s not afraid to be vulnerable and confused,” said Collins, “a young woman who is going through an identity crisis about life and love, and searching for her mother (Lena Headley) and her own voice. At the same time the vampires make it alluring — because people love the unknown. It’s sexy. They’re from an otherworldly place, a fantasy world.”

But director Harald Zwart, she said, wanted a movie that would work in a world of Shadowhunters and demons, or in New York City — the same place, in the case of “Mortal Instruments.”

“He wanted the characters to have the same emotional outcome regardless if they were fantasy characters or real,” said Collins. “And it was important for him that we play them that way.”

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